The present invention relates to fixed an antenna to a radio communication apparatus for mobile communications, and a radio communication apparatus using the same antenna.
In recent years, as a demand for mobile communications has drastically increased, radio communication apparatuses have been developed in a wide variety of forms. An example of this diversity is a radio communication apparatus capable of transmitting/receiving radio waves in multi-ranged frequency bands so that a single radio communication apparatus can handle as much information as possible. Such an apparatus includes an antenna having desirable impedance characteristics over multi-ranged frequency bands.
A mobile phone system is a typical example of mobile communications, which is now widely used all over the world. A frequency bandwidth for the mobile phone system varies by region: Personal Digital Cellular 800 (PDC 800) in Japan uses a frequency in a range of from 810 to 960 MHz. On the other hand, in the West, a range of from 890 to 960 MHz is used for Group Special Mobile Community (GSM), a range of from 1,710 to 1,880 MHz for Personal Communication Network (PCN), and a range of from 1,850 to 1,990 MHz for Personal Communication System (PCS). Generally, for a mobile phone corresponding to each of the multi-ranged frequency bands, a helical antenna element formed of helically wound conductive wire is widely used.
FIG. 12 is a general sectional view of a prior-art antenna for two frequency bandsxe2x80x94for a range of from 890 to 960 MHz of GSM and for a range of from 1,710 to 1,880 MHz of PCN. FIGS. 13 and 14 are graphs that represent frequency characteristics of voltage standing wave ratio (VSWR) showing impedance characteristics.
In antenna 8 shown in FIG. 12, phosphor bronze wire-made antenna element 3 contains linear portion 1 at an inside of helical portion 2, with a top end of linear portion 1 and helical portion 2 being connected to form one piece. Feed metal fitting 6 contains, at its top, recess portion 4 to which antenna element 3 is fixed, and at its bottom, mounting screw portion 5 by which fitting 6 is screwed into a radio communication apparatus. Dielectric resin material-made radome 7 partially covers antenna element 3 and feed metal fitting 6. Fitting 6 is attached to a housing of a mobile phone to establish electric connections with radio-frequency circuitry of the mobile phone, so that antenna 8 can work for two frequency bands mentioned above.
In antenna 8 having the structure above, an electrical length totally gained from linear portion 1 and helical portion 2 of antenna element 3 is adjusted to about xcex/2 in a frequency band for PCN, and is adjusted to about xcex/4 in a frequency band for GSM. Thus, an electrical coupling between linear portion 1 and helical portion 2 of antenna element 3 allows impedance characteristics of antenna element 3 to be optimum in each frequency band.
In prior art antenna 8, the impedance characteristics of antenna element 3 are required by which VSWR is to be at most 3 in each frequency band. However, it has been difficult for this conventional structurexe2x80x94i.e. an antenna element that is helically wound from one end of a straightened phosphor bronze wirexe2x80x94to satisfy this requirement. Suppose that an electrical length of antenna element 3 is adjusted to about xcex/2 in the frequency band for PCN. As shown in FIG. 13, in the frequency band for PCNxe2x80x94between ▾3 and ▾4xe2x80x94impedance characteristics with VSWR kept below 3 can be realized with help of an electrical coupling between liner portion 1 and helical portion 2. On the other hand, in the frequency band for GSMxe2x80x94between ▾1 and ▾2xe2x80x94a range with VSWR maintained below 3 becomes narrower. Now, to eliminate this inconvenience, suppose that the frequency band for GSM (between ▾1 and ▾2) is broadened by changing a diameter or pitch of helical portion 2 and readjusting an electrical length. This adjustment is no good for the PCN bandxe2x80x94it changes an electrical length of antenna element 3 for the frequency band for PCN and an electrical coupling between linear portion 1 and helical portion 2, so that VSWR in the frequency band for PCN (between ▾3 and ▾4) will be undesirably increased to be more than 4. Thus, there has been a problem with structure of the prior art antenna in that transmitting/receiving in either one of the frequency bands has been sacrificed for transmitting/receiving in the other of the frequency bands.
As another drawback, deformation or variations in diameter or pitch of helical portion 2 occurring during a manufacturing process of antenna element 3 can cause variations in impedance characteristics. For these variations, it has been difficult to get desired impedance characteristics. Providing a complicated impedance-matching circuit between an antenna and radio-frequency circuitry may be a measure for suppressing degradation of impedance characteristics due to the variations. However, this is apparently an obstacle to lower prices of mobile phones.
The present invention addresses the problems above. It is therefore an object of the present invention to provide a reliable antenna with high productivity, which is capable of: having an easy adjustment of an electrical length of an antenna element; obtaining good impedance characteristics in desired multi-ranged frequency bands by a single antenna element; and eliminating impedance matching circuitry to minimize variations in impedance characteristics. At the same time, it is another object of the present invention to realize a cost-reduced radio communication apparatus using the antenna.
To achieve the aforementioned objects, the antenna of the present invention includes: an antenna element portion for transmitting/receiving waves in multi-ranged frequency bands; a feed portion for establishing electrical connections between the antenna element portion and radio-frequency circuitry of a radio communication apparatus; a dielectric material core rod mechanically supporting the antenna element portion; and a dielectric material radome partially covering the antenna element portion and the feed portion. The antenna element portion comprises an approximately helical-shaped portion and an approximately meander-shaped portion that are formed concentrically with the core rod.
The antenna of the present invention may be variously embodied as follows.
1) The dielectric material forming the core rod has a relative dielectric constant different from that of the dielectric material forming the radome.
2) A half-round and thin belt-shaped first conductor has a diameter generally equal to that of the core rod. A plurality of first conductors are disposed in parallel from a position close to an end of the core rod in an axial direction, at predetermined spaced intervals, on a front-round surface and rear-round surface of the core rod. Rows of the conductors are placed in a staggered arrangement between the front-round surface and the rear-round surface of the rod. A short and thin belt-shaped conductive plate joins adjacent ends of the first conductors, forming an approximately helical-shaped portion. A plurality of thin belt-shaped second conductors are placed in parallel on the core rod. As in the case of the first conductor, a short and thin belt-shaped conductive plate joins adjacent ends of the second conductors, forming an approximately meander-shaped portion. The approximately meander-shaped portion is disposed close to the approximately helical-shaped portion.
3) The antenna element portion may be formed from a die cutting-processed thin and conductive metal-plate.
4) The antenna element portion may be formed from a press-processed conductive metal-wire made of alloys of copper, or other metals, provided by an electrolytic plating process.
5) The antenna element portion may be formed by subjecting a thin conductive plate to an etching process to form a predetermined pattern, and then press-processing the pattern.
6) The antenna element portion may be formed from a press-processed flexible wiring board having a predetermined pattern formed thereon.
7) The antenna element portion may be formed by printing conductive paste.
8) The antenna element portion may be formed from sintered conductive powder.
9) One end of the approximately helical-shaped portion is joined with one end of the approximately meander-shaped portion so that the approximately helical-shaped portion and the approximately meander-shaped portion are disposed on the rod as a cascaded structure.
10) A position close to a tip of the core rod may have a connecting point, at which one end of the approximately helical-shaped portion and the approximately meander-shaped portion are connected, and at which these two portions seem to be xe2x80x9cfolded overxe2x80x9d. The approximately meander-shaped portion is placed on the rod so as to be parallel to an axis of the approximately helical-shaped portion.
11) A position close to a tip of the core rod may have a connecting point, at which one end of the approximately helical-shaped portion and the approximately meander-shaped portion are connected, and at which these two portions seem to be xe2x80x9cfolded overxe2x80x9d. At least a part of each second conductor of the approximately meander-shaped portion is circularly arc-shaped, having a diameter almost equal to that of the approximately helical-shaped portion. At the same time, an arrangement of the approximately meander-shaped portion is maintained to be concentric with the approximately helical-shaped portion, but having no contact with it.
12) The feed portion may be formed with the antenna element portion as one piece.
13) A dielectric material radome, which partially covers the antenna element portion and the feed portion, may be removed.
According to the present invention, each electrical length and its ratio of the approximately helical-shaped portion and the approximately meander-shaped portion can be defined easily. As compared with a conventional antenna, the antenna of the present invention can easily provide desired multi-ranged frequency bands with optimal impedance characteristics. This allows the antenna to be compact and cost-reduced, having advantages of wide frequency range, high antenna gain, and high reliability.
The present invention covers not only a radio communication apparatus equipped with the antenna, but also a radio communication apparatus equipped with two antennas for diverse communications.